US President Donald Trump struck a defiant tone last Friday, saying trade wars were good and easy to win, after his plan to put tariffs on imports of steel and aluminium triggered global criticism and a slide in world stock markets.

US President Donald Trump struck a defiant tone last Friday, saying trade wars were good and easy to win, after his plan to put tariffs on imports of steel and aluminium triggered global criticism and a slide in world stock markets.

The EU raised the possibility of taking countermeasures, France said the duties would be unacceptable and China urged Trump to show restraint. Canada, the biggest supplier of steel and aluminium to the US, said it would retaliate if hit by US tariffs. US stocks had opened sharply lower on Friday after Trump said on Thursday that a plan for tariffs of 25pc on steel imports and 10pc on aluminium products were designed to safeguard American jobs in the face of cheaper foreign products and would be formally announced next week.

"When a country (USA) is losing many billions of dollars on trade with virtually every country it does business with, trade wars are good, and easy to win," Trump tweeted on Friday. "Example, when we are down $100bn with a certain country and they get cute, don't trade any more, we win big. It's easy!" he wrote. It was not clear which country he was referring to.

The prospect of retaliation from Canada, China and Europe sent world stocks tumbling as investors turned to traditional safe havens such as government bonds, gold and the Japanese yen. "It is a real worry because Europe is an open global economy so it isn't just about US versus China," said Ian Ormiston, European equity fund manager at Old Mutual Global Investors. "And we will see retaliation, there are no two ways about it."

Home appliance maker Electrolux said it was delaying a $250m expansion of its plant in Tennessee as it was worried US steel prices would rise and make manufacturing there less competitive.

But Turkey's leading steelmaker, Borusan Holding, said it might expand its US steel pipe factory in Texas because of the proposed tariffs.

The European Commission called the US tariffs a blatant intervention that amounted to protectionism and promised to act "firmly" in response.

The EU, seeing itself as a counterweight to a protectionist-leaning Trump, made no mention of retaliation but spoke of countermeasures that conform with World Trade Organization (WTO) rules.

"We see international trade relations as a win-win situation," a European Commission spokesman said. "We don't see this as a situation where, like in a zero-sum game, one party loses because another party wins. Trade is beneficial for everyone. It needs to take place on the basis of rules and these rules are in place."